Mobile phones provided with a navigation function utilizing GPS (Global Positioning System) to display a geographical position of the present location have been put into practical use. In this type of mobile phone, generally a geomagnetism sensor is mounted. It is possible to display a bearing together with the present location. For example, by the so-called “heading up” display method rotating a display direction of a map to match an advancing direction may be used to display the present position and the advancing direction in a manner easily understandable to a user.
A geomagnetism sensor uses, for example, a magnetoresistance device or other magnetism detection device to detect the intensity of geomagnetism in a plurality of directions (usually biaxial directions or triaxial directions). However, geomagnetism is very weak, therefore a detection value of a geomagnetism sensor is easily affected by other magnetism. In particular, magnetism generated in parts inside an electronic apparatus in which a geomagnetism sensor is mounted becomes a major cause of error of the detection value of the geomagnetism. The magnetism generated inside an electronic apparatus creates a constant magnetic field inside the electronic apparatus no matter which direction the electronic apparatus is directed in, therefore this causes a fixed error (offset) in the detection value of the geomagnetism. In order for the geomagnetism sensor to detect the geomagnetism with a good precision, calibration for estimating this offset and eliminating it from the detection value of the sensor becomes indispensable. Patent Documents 1 to 8 disclose technologies concerning calibration of a geomagnetism sensor mounted in a portable electronic apparatus.
On the other hand, IC chips engaging in non-contact communication with external reader/writer devices are becoming popular. IC cards in which these are embedded are being widely used for train and bus tickets, bank cash cards, electronic money media, and so on. In recent years, mobile phones having such IC card functions built-in have appeared and are attracting attention (see, for example, Patent Document 9).
Patent Document 1: Japanese Patent Publication (A) No. 2005-291931
Patent Document 2: Japanese Patent Publication (A) No. 2005-291932
Patent Document 3: Japanese Patent Publication (A) No. 2005-291933
Patent Document 4: Japanese Patent Publication (A) No. 2005-291934
Patent Document 5: Japanese Patent Publication (A) No. 2005-291935
Patent Document 6: Japanese Patent Publication (A) No. 2005-291936
Patent Document 7: Japanese Patent Publication (A) No. 2005-291937
Patent Document 8: Japanese Patent Publication (A) No. 2005-291938
Patent Document 9: Japanese Patent Publication (A) No. 2003-16398